Recently having symlinked '/usr/share' to an ext3 partition on the internal memory card (6 gb, with mmc2 (mmcblk0p1) @ 2 gb)), I felt confident in getting a zoom-level-5 set of maps for the greater Bay Area. It amounted to a little over 700MB and 12,000 maps. Redirected to save the maps to the removable memory card (8 gb) Maemo Mapper did fine crunching it ("Processing maps") but on returning after a couple hours, the unit was grey-screened (I had it plugged in to a/c, so it was grey instead of black).

Fortunately I had just backed-up so reflashing and re-symlinking/mount-set-up was all that was required. Going forward I'll just take a few maps here and there, unless anyone has some convincing ideas. For example, perhaps there is some other spot that Maemo Mapper also saves data to that filled up a critical directory tree.